Biff: Look, Lorraine, you walk out that door and I won't only cut off you, I'll cut off your kids.
Lorraine: You wouldn't!?
Biff: Oh, wouldn't I? First your daughter, Linda. I'll cancel all her credit cards. She can settle her debts with the bank all by herself. Your idiot son, Dave. I'll get his probation revoked. And as for Marty. Well, maybe you liked to have all three of your kids behind bars just like your brother Joey. One big happy jailbird family.
Biff: Go ahead, kid. Jump. A suicide will be nice and neat.
Marty: What if I don't?
Biff: [raising gun] Lead poisoning.
Marty: What about the police, Biff? They're gonna match up the bullet with that gun.
Biff: Kid, I own the police. Besides, they couldn't match up the bullet that killed your old man.
Marty: You son of a...
[Biff pulls back on the gun's hammer.]
Biff: Suppose it's poetic justice. Two McFlys with the same gun.
Biff: Oh! Nice dress, Lorraine. Although, I think you'd look better wearing nothing at all.
Lorraine: Biff, why don't you take a long walk off a short pier?
Biff: Hey listen, Lorraine. Now that I got my car all fixed up I figured I cut you a break and give you the honor of going with the best looking guy in school.
Lorraine: Yeah, well, I'm busy.
Biff: Oh, yeah? Doing what?
Lorraine: Washing my hair.
Biff: Oh, that's about as funny as a screen door on a battleship.
Marty: Screen door on a submarine, you dork.
Marty: Nobody calls me chicken.
Red the Bum: Crazy drunk pedestrians!
Doc: Roads? Where we're going, we don't need roads.
Marty: You mean I'm going to see where I live? I'm going to see myself as an old man?
Doc: No, no, no, Marty, that could result in a...[gasps]. Great Scott! Jennifer could conceivably encounter her future self! The consequences of that could be disastrous.
Marty: Doc, what do you mean?
Doc: I foresee two possibilities. One, coming face-to-face with herself 30 years older would put her in shock and she'd simply pass out. Or two, the encounter could create a time paradox, the result of which could cause a chain reaction that would unravel the very fabric of the space-time continuum and destroy the entire universe! Granted, that's a worse-case scenario. The destruction might in fact be very localized, limited to merely our own galaxy.
Marty: Well, that's a relief.
Data: Hey McFly, you bojo, those boards don't work on water!
Whitey: Unless you've got POWER!
Lorraine: Biff Tannen, I wouldn't be your girl even if...even if you had a million dollars.
Doc: The time-traveling is just too dangerous. Better that I devote myself to study the other great mystery of the universe...women!
Young Biff: Manure! I HATE manure!
Old Biff: I have a little something for you. You do want to be rich, don't you?
Young Biff: Oh, yeah. Sure. That's rich. You're gonna make me rich.
Old Biff: You see this book? This book tells the future. It tells the outcome of every major sports event 'til the end of the century. Football, baseball, horse races, boxing. The information in here is worth millions, and I'm giving it to you.
Young Biff: That's very nice. Thank you very much. Now why don't you make like a tree, and get out of here?
Old Biff: It's LEAVE, you idiot!"Make like a tree and leave." You sound like a damn fool when you say it wrong!
Marty: That's right, Doc. November 12,1955.
Doc: Unbelievable, that old Biff could have chosen that particular date. It could mean that that point in time inherently contains some sort of cosmic significance. Almost as if it were the junction point for the entire space-time continuum. On the other hand, it could just be an amazing coincidence.
Doc: Marty! What in the name of Sir Isaac H. Newton happened here?
Answer: At the end of the first film, Doc says, "what the hell" in response to the letter Marty gave him. So this shows it is not that strong a conviction, especially in the face of definite knowledge about something bad happening. It is also a way for Doc to repay Marty.
MasterOfAll